Remove window variable from ExecJS environment

[NGMarmaduke]

Fixes #614

Defining window on the server can cause major issues when using 3rd party libraries that perform type of checks on the window variable to detect the presence of a browser environment.

A common check for presence of the browser is:

if (typeof window !== 'undefined') { // do browser stuff }

This PR removes the requirement for window to exist on the server. It will however be a breaking change for applications that implicitly expect the existence of window in all javascript environments.

The definition of window on the server could potentially be made a configuration option to mitigate errors.

This PR also updates React to version 15.3.2

[NGMarmaduke]

Warning: unmountComponentAtNode(): The node you're attempting to unmount was rendered by another copy of React.

Looks like running into the same error as on #611

[NGMarmaduke]

Removed the update to React

[rmosolgo]

I think this is Ok, but we need to document the change so that people who currently depend on window (using it as the global namespace) know how to upgrade.

I checked coffeescript, it looks like it compiles to something compatible:

@test = false 

to

(function() { this.test = false }).call(this)

(I thought it might use window as @, but looks like not)

[NGMarmaduke]

Indeed, I'm attempting to apply this update to our app to see if its even feasible / sensible to make this change

[rmosolgo]

How did it go applying this to your app?

[rmosolgo]

I hope it went ok :P But I agree, making server render pretend to be a browser env only makes it worse down the line.

[rmosolgo]

🚢 in 1.10.0, thanks!

[dbackeus]

Not actually sure how to fix the errors we get after upgrading to 1.10.0:

 Failure/Error: <%= react_component "ComponentName", { ActionView::Template::Error: ReferenceError: window is not defined # (execjs):44062:3 # (execjs):44064:2 

The components we use do not reference window explicitly as far as I can see (but are defined as @ComponentName = React.createClass(...)).

The CHANGELOG mentions manually adding window = this but not sure where to do that?

[rmosolgo]

@dbackeus Do those errors come from server rendering?

Do you have a server-rendering manifest (some file that requires all the components for server rendering)? If so, you can add it to that file, for example:

//= require components  // polyfill `window` variable for server rendering environments: var window = this 

If that doesn't help, can you share the lines of code that reference window? A better (or earlier) polyfill may be needed

[piratefsh]

FYI I had the same window is not defined issue and tried to set var window = this after the components were required but that still gave the error. What worked was to set window before the React was required. In my case, React was required in my react_app file.

e.g.

prerender_polyfill.js

// polyfill for prerendering. must be set before requiring react var window = this;

components.js

//= require prerender_polyfill //= require react_app

[piratefsh]

Since window is needed to even load React, shouldn't this be mentioned in the README setup?